U.S. patent number 5,293,755 [Application Number 07/987,776] was granted by the patent office on 1994-03-15 for air conditioning load management control system.
Invention is credited to Charles V. Thomas.
United States Patent |
5,293,755 |
Thomas |
March 15, 1994 |
Air conditioning load management control system
Abstract
A load management control system is provided for an air
conditioner. The system includes an outdoor temperature sensor for
sensing outdoor temperature of the outside of an enclosure to be
air-conditioned and an indoor temperature sensor for sensing an
indoor temperature of the enclosure. A device is provided for
determining a difference in output of the indoor and outdoor
temperature sensors. A device is provided for comparing the
difference in output of the indoor and outdoor temperature sensors
with a reference input. The system further includes a device for
detecting an external controlling signal from an input device
coupled to the system. A control device is provided for controlling
an air conditioner control circuit based upon input from the
comparing device and the detecting device. When an allowable
temperature differential is exceeded, the controlling device opens
at least one contact to interrupt the air conditioner control
circuit so as to reduce electrical load. The controlling device
closes the contact to restore the operation of the air conditioner
control circuit when the temperature differential is no longer
exceeded.
Inventors: |
Thomas; Charles V. (Ashland,
VA) |
Family
ID: |
25533544 |
Appl.
No.: |
07/987,776 |
Filed: |
December 9, 1992 |
Current U.S.
Class: |
62/208; 236/91R;
307/39 |
Current CPC
Class: |
G05D
23/1923 (20130101) |
Current International
Class: |
G05D
23/19 (20060101); F25B 041/00 () |
Field of
Search: |
;307/39 ;62/208
;236/91D,91R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0003942 |
|
Jan 1986 |
|
JP |
|
0021313 |
|
Jan 1990 |
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JP |
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Primary Examiner: Wayner; William E.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A load management control system for an air conditioner
comprising:
an outdoor temperature sensor for sensing outdoor temperature of
the outside of an enclosure to be air-conditioned;
an indoor temperature sensor for sensing an indoor temperature of
the enclosure;
means for determining a difference in output of said indoor and
outdoor temperature sensors;
means for comparing said difference in output of said indoor and
outdoor temperature sensors with a reference input;
means for detecting an external controlling signal from an input
device coupled to said system;
means for controlling an air conditioner control circuit based upon
input from said comparing means and said detecting means, whereby,
when an allowable temperature differential is exceeded while the
external controlling signal is detected, said controlling means
interrupts operation of said air conditioner control circuit so as
to reduce electrical load, said controlling means restoring the
operation of said air conditioner control circuit when said
temperature differential is no longer exceeded.
2. A load management control system as claimed in claim 1, further
comprising:
means for comparing said inside temperature to a preset limit to
determine whether said inside temperature exceeds said preset
limit; and
means for blocking control of said controlling means when said
indoor temperature exceeds said preset limit.
3. A load management control system as claimed in claim 1, further
comprising means for ramping inside temperature changes so as to
not take place faster than a predetermined rate when a sudden drop
in outside temperature occurs.
4. A load management control system as claimed in claim 1, wherein
said external control device is a load management controller having
a dry contact.
5. A load management control system as claimed in claim 1, wherein
said external control device is a communications subsystem.
6. A load management control system as claimed in claim 1, wherein
said determining means and said comparing means are each
operational amplifiers analog circuits.
7. A load management control system as claimed in claim 1, wherein
said controlling means controls an output relay, said relay being
connected to said air conditioner control circuit.
8. A load management control system as claimed in claim 1, wherein
said determining means, said comparing means, said detecting means
and said controlling means is a microprocessor.
9. A method of controlling an air conditioning system comprising
the steps of:
operating the air conditioning system at full load;
determining a temperature outside an enclosure to be air
conditioned;
determining a temperature inside said enclosure;
determining the difference between said inside and outside
temperatures;
interrupting a control circuit of a cooling device of said air
conditioning system when said difference exceeds a predetermined
differential so as to reduce electrical load; and
resuming operation of said cooling device at full load when said
inside temperature rises to reduce the difference between said
inside and outside temperature below said predetermined
differential.
10. A method of controlling an air conditioning system as claimed
in claim 9, wherein the steps of determining a difference between
inside and outside temperatures, and interrupting and resuming the
operation of said cooling device are is accomplished by an analog
circuit.
11. A method of controlling an air conditioning system as claimed
in claim 9, wherein the steps of determining a difference between
inside and outside temperatures, and interrupting and resuming the
operation of said cooling device are is accomplished by a digital
circuit.
12. A method of controlling an air conditioning system comprising
the steps of:
establishing an inside temperature set point;
operating the air conditioner at full load;
determining a temperature outside an enclosure to be air
conditioned;
determining a temperature inside said enclosure;
determining the difference between said inside and outside
temperatures;
interrupting a control circuit of a cooling device of said air
conditioning system when said difference exceeds a predetermined
differential so as to reduce electrical load; and
preventing said indoor temperature from exceeding a predetermined
value greater than said inside temperature set point by cooling
said enclosure while at a reduced load; and
resuming operation of said cooling device at full load when said
inside temperature rises to reduce the difference between said
inside and outside temperature below said predetermined
differential.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system for controlling the
operation of an air conditioning system, and more particularly to a
load management control system for reducing air conditioning load
during peak periods.
2. Description of the Art
The control of temperature in enclosed areas such as residential
and commercial buildings is important for comfort of the
inhabitants as well as for efficiency. Energy considerations become
important when the outside temperature substantially exceeds an
indoor temperature set point. In conventional air conditioning
systems, automatic controls maintain cooling levels in a selected
range. Most thermostatic controls permit the user to set a
prescribed temperature above which the system will energize to cool
the building. However, when the outdoor temperature greatly exceeds
the indoor temperature set point, a substantial energy load is
required to maintain the indoor temperature. As a result, excessive
cooling of the building adversely effects the physical condition of
building occupants, and energy is wasted since the air conditioner
is operated to provide an energy load in excess of that required to
maintain a comfortable interior temperature.
Prior systems have attempted to control the indoor temperature
based upon the outdoor temperature. U.S. Pat. No. 4,289,272
discloses a temperature control apparatus which operates by
calculating a desired indoor temperature using a predetermined
linear function of outdoor temperature.
U.S. Pat. No. 4,089,462 discloses a temperature control system for
shifting the indoor temperature set point in accordance with
outdoor temperature. Heating and cooling input to a room of a
building is controlled based upon the outdoor temperature and a
K-Factor, to maintain a constant indoor temperature. However,
careful analysis of the dwelling heat transfer ability is required
for such control.
While the control systems described in the above references provide
a significant improvement in air conditioning systems, these
systems require either complicated algorithms or a study of
particular building characteristics to facilitate temperature
control.
It would be desirable, therefore, to provide a simple and more
effective means of controlling the load requirements for an air
conditioning system based upon a difference between indoor and
outdoor temperature.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an air conditioning
load management control system which automatically provides load
reduction that tracks the increase of outdoor temperature above the
indoor temperature.
It is another object to provide a control system which provides
consistent control among users without the need to address
particular characteristics of the user's dwelling or air
conditioning equipment and without employing a special
algorithm.
It is a further object of the invention to provide an air
conditioning load management system that can be easily installed
and maintained.
These objectives are obtained in accordance with the principles of
the present invention by providing a load management control system
for an air conditioner including an outdoor temperature sensor for
sensing outdoor temperature of the outside of an enclosure to be
air-conditioned and an indoor temperature sensor for sensing an
indoor temperature of the enclosure. A device is provided for
determining a difference in output of the indoor and outdoor
temperature sensors. Another device is provided for comparing the
difference in output of the indoor and outdoor temperature sensors
with a reference input. The system further includes a device for
detecting an external controlling signal from an input device
coupled to the system. A control device is provided for controlling
an air conditioner control circuit based upon input from the
comparing device and the detecting device. When an allowable
temperature differential is exceeded, the controlling device opens
at least one contact to interrupt the air conditioner control
circuit shutting down the air conditioner's compressor so as to
reduce electrical load. The controlling device closes the contact
to restore the operation of the air conditioner control circuit
when the temperature differential is no longer exceeded.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an air conditioning load
management control system provided in accordance with the
principles of the present invention;
FIG. 2 is a schematic installation diagram of an air conditioning
load management control system provided in accordance with the
principles of the present invention;
FIG. 3 is a schematic diagram of an analog circuit of the present
invention;
FIG. 4 is a schematic diagram of an air conditioning load
management control system with optional high indoor temperature
limit;
FIG. 5 is a schematic diagram of a digital load management control
system provided in accordance with the principles of the present
invention;
FIG. 6 is a logic flow diagram for a digital load management
control system of the present invention.
FIG. 7 is a schematic diagram of an analog circuit of the present
invention having selectable fixed set points;
FIG. 8 is schematic diagram of a relay driver circuit provided in
accordance with the principles of the present invention;
FIG. 9 is a schematic diagram of a digital air conditioner load
management control using a microcontroller in accordance with the
principles of the present invention;
FIG. 10 is a graph showing the operation of the load management
control system having a ramp-down feature.
FIG. 11 is a graph showing the operation of the load management
control system having a ramp-down feature.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The load management control system 10 will now be described with
reference to FIGS. 1-3, which are schematic diagrams of the
components of the system 10, according to the present
invention.
The system 10 includes a conventional indoor temperature sensor 12,
which is a solid state transducer that provides an output voltage
proportionate to temperature. In the illustrated embodiment, a
National Semiconductor LM335 Precision Temperature Sensor is used
having a calibration potentiometer (R2). However, other sensors
that produce a linear output voltage with respect to temperature
may be used, such as thermistors. The sensor 12 should preferably
be calibrated to an accuracy of 0.15 degrees Fahrenheit or better
when operated with a mid-scale voltage output of approximately 5
volts. In the illustrated embodiment (FIG. 2), the indoor
temperature sensor 12 is connected to the air conditioner load
control circuit 52 by a twisted wire pair 16. No external power
wiring is required. The sensor 12 can be mounted in an enclosure
and sized smaller than a typical household thermostat.
An outdoor temperature sensor 18 is provided outside the enclosure
to be air-conditioned. The outdoor temperature sensor 18 is
electrically identical to the indoor temperature sensor 12. In the
illustrated embodiment, a second LM335 Precision Temperature Sensor
is used having a calibration potentiometer (R1). The outdoor sensor
18 is preferably encapsulated in a waterproof module (not shown)
and mounted in a small vented outdoor box. The outdoor temperature
sensor 18 is also electrically connected to the air conditioning
load control circuit 52 by a twisted wire pair 16.
A differential amplifier circuit 20 is provided which produces a
voltage level corresponding to the difference in output of the
indoor sensor 12 and outdoor sensor 18. In the illustrated
embodiment, differential amplifier circuit 20 is a conventional
operational amplifier such as National Semiconductor LM324 or a
generic 741 operational amplifier. The output of amplifier 20 is
sent to set point level control 22 via line 21. As shown in FIG. 3,
the differential amplifier circuit components include an
operational amplifier 23, resistors R3, R4, R5, R6, R7, R8, R9 and
capacitor C1.
The set point control 22 is built around a second operational
amplifier 33 integrated circuit. When the input received from
differential amplifier circuit 20 exceeds a certain fixed voltage,
such as 0 to 1 volts with reference to a Midpoint Voltage Reference
(used as a center reference which is exactly half of the power
supply voltage), supplied from adjustable reference voltage source
24 (shown as R12 in FIG. 3), the set point control 22 generates a
positive voltage level at the input of the control logic 26 (FIG.
1). This will initiate load control until the inside temperature
raises to a point where the input voltage drops below the set point
value if a closed circuit is present across external contact
control input 32. The set point can be field adjusted to a
predetermined temperature differential before the system 10 begins
shedding load. The system may have more than one set point, any of
which can be selected by external contacts. FIG. 3 shows a single
adjustable set point using potentiometer R12 to calibrate the
single value. In the alternative, FIG. 7, shows selection of fixed
points approximately 4 degrees apart using switch S1. A series of
fixed resisters replaces potentiometer R12. With this arrangement,
various temperature differential arrangements can be selected by
closing the appropriate contact as required for prevailing
conditions. For example, load management may be required during
moderately warm outdoor temperatures. Selection of a lower
temperature differential will make the device more effective under
these operating conditions. Switch S1 may be replaced with external
contacts to permit remote selection.
In the illustrated embodiment, the adjustable reference voltage
source 24 is developed by using precision resistors across a
regulated voltage power supply. As shown in FIG. 3, the adjustable
reference voltage source 24 includes resistors R11, R12, R13 and
R14, and the set point control 22 includes an operational amplifier
33, R10, and R15.
As shown in FIG. 1, an external control input circuit 30 is used to
determine when to enable or disable the function of the control via
a remote control device 32. In the preferred embodiment, a
preferably optically isolated input circuit is used to detect a dry
contact closure for initiating load control. The load management
control system 10 is intended for interfacing with existing
conventional load management systems. Existing load management
systems use the opening (or closing) of a contact to perform
control functions. This contact is typically electrically isolated
to permit it to be placed in the circuits of the user equipment
which supply operating voltages. The dry contact design is
preferable since it enables easy connection to these devices.
However, any type of input, for example, logic levels from a
microprocessor or decoder may be used provided the proper interface
circuitry is present. As shown in FIG. 3, the control contact of
the remote control device 32 is connected in series with the output
control relay 34. If no external load controller 14 is available,
additional circuitry can be added to permit the circuit to function
with components of basic communication subsystems, such as paging
radios or telephone communications that are capable of providing
logic output based on received signals. The load management system
can be modified to operate from any such communication subsystem by
obtaining a subsystem that produces unique logic levels for
enabling and disabling the control, based on received signals and
developing interface circuitry to translate output from the
communication subsystem into logic levels for enabling and
disabling the load management control. FIG. 8 shows an example of a
relay driver circuit for such purpose.
The control logic circuit 26 receives the input from the set point
control 22 and the external control input circuit 30 to determine
when to open output relay contacts 34. Preferably, the control
logic circuit 26 also contains circuitry necessary to drive the
output relay 34. If the allowable temperature differential is
exceeded while the control contact of the remote control device 32
is closed, the control logic circuit 26 will open the contact 34
and interrupt the air conditioner compressor control circuit 36.
The output relay 34 provides a contact that is connected in series
with the air conditioner compressor control leads to turn off the
unit during periods when load management is required.
FIG. 10 illustrates the operation of the load management system
10.
As shown, the outside temperature is tracked by the inside
temperature. The system 10 interrupts the control circuit of the
compressor 36 when the outside temperature exceeds the inside
temperature by a set differential. The system provides for
automatic load shedding and restoration. As the outside temperature
increases, the constant differential causes the indoor temperature
to track the outdoor temperature resulting in a proportionate
shedding of load. Load restoration automatically occurs when the
outside temperature falls to a point where it is less than the
established differential plus the indoor temperature. Consequently,
no special algorithms are required in the system to deliver smooth
load shedding restoration.
An optional high indoor temperature limit control may be provided
in the system 10 to keep the indoor temperature from exceeding a
preset value. This feature can be used to limit customer discomfort
should the outdoor temperature rise to a level where the inside
temperature becomes excessive.
As shown in FIG. 10, the set point may be set at a value (i.e.,
83.degree. F.) which permits some cooling while providing load
reduction. This feature makes the placement of the outdoor
temperature sensor less critical.
As shown in FIG. 4, an optional differential amplifier circuit,
indicated at 40, is provided when high limit indoor temperature
control is desired. This circuit compares the inside temperature to
a fixed reference 42. The output is used to determine whether the
inside temperature has exceeded a preset limit by the set point
control 44. An operational amplifier, similar to operational
amplifier 23 is used for this comparison function. This circuit is
not required if high limit indoor temperature control is not
required.
The output of the fixed reference 42 is used by the differential
amplifier circuit 40 for comparison with the voltage of the input
temperature sensor to determine when the high level limit has been
exceeded. This circuit can be adjustable, allowing calibration of
the high indoor temperature limit. The set point control 44 uses an
operational amplifier to generate a voltage, should the high
temperature limit be exceeded by the indoor temperature. The set
point control 44 is determined by comparing the output of
differential amplifier circuit 40 to adjustable reference 46. The
output of the set point control 44 is sent to the control logic
circuit 26 and when the set point is exceeded, the control logic
circuit will block control of the air conditioner compressor.
Digital system control may also provide the same function as the
above analog control by using microprocessor based functions.
With reference to FIG. 5 and 6, a digital load management control
system 110 is shown. An indoor temperature sensor 112 and an
outdoor temperature sensor 118 are provided each which produce an
output voltage proportionate to temperature being sensed at any
given point in time. These temperature sensors are substantially
similar to those discussed above at 12 and 18.
The output of the temperature sensors 112, 118 is sent to
conventional analog to digital converters 120 to convert the analog
voltages into digital representations, which can be used by the
microprocessor 126. Latch circuits 122 are provided to interface
the digital outputs of the analog to digital converters 120 to the
microprocessor 126 as well as the remote control input and relay
control output of the control system. The external remote control
input is interfaced to the latch circuit 122 by interface circuit
124 to provide proper signal conversion and protection against
abnormal conditions such as surges. The latch circuits 122 permit
the microprocessor 126 to read and store data until it is ready for
processing or a change of state.
As shown in FIG. 5, an external remote control input 130 is
provided to permit an external remote control system to enable or
disable the function of load management control, which is similar
to the analog control input 30. A relay driver 132 is used to
develop adequate power from the output latch circuitry to drive the
output relay 134. The output relay 134 serves the same function as
the output relay of the analog system discussed above.
A conventional microprocessor 126 controls all operations of the
digital load management control system 110 including data
acquisition from input devices and control of the output relay 134,
based on instructions in a control program. The microprocessor 126
preferably includes the ability to perform analog to digital
conversion as well as digital processing functions. As an
alternative to the circuit of FIG. 5, FIG. 9 shows a microcontrol
unit 140 (Motorola MC68HC11EO or equivalent) which includes the
microprocessor 126. A Read Only Memory (ROM) device 136 is also
provided. Physical storage of the control program is implemented in
the read only memory or other non-volatile storage media in order
to avoid corruption by abnormal operating conditions.
As shown in FIG. 6, the control program contains routines for
performing calculations and logic functions implemented by hardware
in the analog control. These functions include:
(a) reading data from temperature sensors,
(b) calculating the difference between indoor and outdoor
temperatures;
(c) providing a reference value for calculating the reference
control function;
(d) monitoring of the remote control input to determine if the load
management function should be active or inactive; and
(e) generating a control output based upon the values from the set
point control function and remote control input.
Multiple fixed settings can be provided for the digital system by
using several inputs for remote control and programming the system
to produce various temperature differential settings, depending on
which input receives a control signal.
Microprocessor based digital air conditioning load management
control offers significant flexibility over analog design for the
support of optional features. The high temperature set point can be
implemented in the program by comparing the value of the inside
temperature to a set value in program memory and limiting load
reduction to the predefined maximum value.
A microprocessor based control will also permit ramping of inside
temperature changes so they cannot take place faster than a
predetermined rate. This feature is beneficial in limiting the rate
of change for inside temperatures in the event of sudden weather
changes. A sudden drop in outside temperature could result in a
corresponding drop in the differential between inside and outside
temperatures causing the air conditioning system to operate
continuously until either the thermostat is satisfied or the
temperature differential is reestablished. The use of a ramping
function to gradually decrease the inside temperature under these
conditions will maintain the effectiveness of the load control
until normal operating conditions are established after a sudden
weather change. This function can be implemented in software by
dropping the inside temperature in small increments that are timed
to slow the drop of the inside temperature. This feature is shown
in FIG. 11 below.
Thus, either an analog or digital approach to provide load
management produces the same result. The system 10 is remotely
controlled to provide load control when required. This is
accomplished by controlling a contact closure from an existing load
management controller 14. The illustrated embodiment is for a dry
contact external control. However, as stated above, the load
management control system can operate from other types of input if
proper interface circuits are included. As discussed above,
additional circuitry may permit the system 10 to be integrated into
other systems such as radio paging. Since the system 10 has the
ability to control through an entire load shed cycle with only one
command, the system 10 may share communication facilities with
other applications without significant performance degradation.
Referring to FIG. 2, the installation of the load control
management system is shown. The air conditioner load control
circuit 52, which includes the integrated circuit, is installed
adjacent to or inside of the load management controller 14. The air
conditioner load control circuit is connected to the controller 14.
The outdoor temperature sensor 18 is preferably installed on the
north side of the building and is connected to the air conditioner
load control circuit 52 directly. The indoor temperature sensor 12
is installed on the inside wall of the building using the same
general guidelines for installing a thermostat. A location close to
the outdoor temperature sensor is preferred to limit the amount of
wiring required. The indoor temperature sensor is also connected to
the air conditioner load control circuit. The output relay 34 is
then connected in series with 24 volt compressor control
circuit.
Once installed, the system 10 can provide approximately 30 percent
reduction in air conditioning load based upon an indoor temperature
rise from 75 degrees to 83 degrees Fahrenheit for an outside
temperature rise of 100 degrees Fahrenheit.
It can be seen that the system 10 of the present invention provides
an effective means of reducing air conditioner load requirements
during peak periods without the use of complicated algorithms or
the need to address the specific building characteristics when the
system is installed.
While the invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiment, it is understood that the invention is not limited to
the disclosed embodiment but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
* * * * *